The present invention relates to a method and an apparatus for dynamic power control for a vehicle with a fuel cell which supplies electrical energy to the vehicle.
An article by P. Agarwal in IEEE Transactions on Power Apparatus and Systems, 88 (1969) 2, pp. 88-93, proposes a vehicle which is driven by an electric motor supplied with electrical energy via fuel cells. In order to control the power of the electric motor, and thus of the vehicle, it is suggested to transform the fixed voltage supplied by the fuel cell with the aid of a voltage transformer as a function of the power request. The disadvantage with this system is the low efficiency in the partial-load range.
Therefore, an object of the invention is to provide a method and an apparatus in which the power of a vehicle with a fuel cell can be controlled dynamically and with optimum utilization of the electrical energy produced.
The foregoing object has been achieved in accordance with the present invention by providing that the maximum electrical power made available by the fuel cell is fed to the electrical drive unit, and the power is set by controlling the oxidant flow rate, i.e. air intake flow rate.
By virtue of the control of the vehicle power by way of the rate of oxidant flow, it is ensured that the entire electrical energy made available by the fuel cell is supplied to the drive unit under all operating conditions, and the energy used is thus utilized to an optimum degree. For this purpose, it is within the scope of the present invention that the prescribed set value for the power is to be limited as a function of operating parameters. As a result, the fuel cell is prevented from producing more electrical energy than the drive unit can instantaneously absorb because of, for example, overloading. In order to prevent the drive unit requiring more electrical energy than the fuel cell is instantaneously supplying, it is, of course, also necessary for the set value which is transmitted to the drive unit by the driver to be corrected or limited. The arrangement of a compressor with an adjustable rotational speed in the oxidant intake line constitutes one simple and advantageous way of controlling the oxidant flow rate.